Heretofore, radiologists manually adjusted the brightness and contrast of the display image to suit the radiologists visual preference, and to accommodate the nature of the internal structure being examined. Variation in X-ray intensity at the detector camera varied due to such factors as manufacturing tolerances, tube aging, detector position, and patient body type. This radiation variation caused shifts in the greyscale of the camera image. An increase in radiation promoted an over exposed light images, and a decrease in radiation promoted an under exposed dark image.
A calibrating wedge of known attenuation was imaged permitting the radiologist to manually calibrate the display image. The calibrating wedge had a thick high attenuation end simulating bone structure which attenuated radiation producing an under exposed light image. The calibrating wedge also had a thin low attenuation end simulating soft tissue which readily passed radiation producing an over exposed dark image. The radiologists used these light and dark images (and the greyscale tones therebetween) as a guide to adjusting the display image.